It is today usual to automatically achieve head displacement and cassette loading and ejection in a tape player, for example, by use of a motor power. Such a system is remarkably advantageous because a variety of changeover operations are achieved with an extremely small power called "feather touch" as compared to an old-fashioned mechanism which requires a considerably large manual power for changeover operations.
To effect such automatic changeover operations, it is usual to employ a mechanism comprising a drive gear driven by a motor, a driven gear driven by the drive gear and having an engagement portion and a recess partly breaking the tooth train thereof, and a stopper for engagement with the engagement portion of the driven gear so that the recess faces the drive gear when the stopper engages the engagement portion, thereby cancelling the linkage relation between the drive gear and the driven gear. To recover the linkage relation from the disconnected state, the driven gear is biased by a spring, for example, so that when the stopper is disengaged from the engagement portion of the driven gear, the driven gear is rotated up to an angular position where the tooth train meshes the drive gear.
However, since the prior art mechanism having the above-described system requires a complicated and delicate structure to ensure disconnection and connection of the linkage elements, it cannot always achieve a reliable operation. For example, the spring adapted to apply a rotational force to the driven gear cannot always achieve its role because the force to rotate the driven gear becomes zero when a point for receiving the spring force is just on the line of the biasing force of the spring, or extremely small when the point is not so far from the line. This affects an operational stroke of an operating member responsive to the rotation of the driven gear for controlling other mechanisms, thereby causing a phenomenon that the operating member cannot achieve its expected controlling operation when the force to rotate the driven gear is substantially zero. In order to assure a predetermined operational stroke of the operating member to prevent the phenomenon, it will be necessary to employ a larger driven gear so that said extremely small rotation of the driven gear is out of the operational stroke of the member. This invites a bulky system and excessive movement of the mechanism. Particularly, in case that the driven gear is adapted to bring a head and pinch rollers ahead, it is important to effect their reliable and proper pressure contact with a tape within the operational stroke of said member and to detach the interlocking relation as maintaining the pressure contact of the head and pinch rollers for calling playback or recording mode. However, if said pressure contact is achieved and the interlocking connection is cancelled at a time when the driven gear is not provided with rotational force, i.e. when the point receiving the spring force is placed on the line of the biasing force, the linkage will not be actuated unless some other force is applied thereto, thereby greatly reducing the advantages of the automatically operative system.